The present invention relates to contact lenses utilized in ophthalmic surgery and, more particularly, to contact lenses that improve the delivery of laser energy during ophthalmic surgery.
Eye diseases such as glaucoma inhibit the free circulation of aqueous humor within the eyeball. One method of treating diseases such as glaucoma is to perforate eye tissues such as the iris to promote the flow of aqueous humor. Lasers have been effectively employed for iris perforation. When laser iridectomy was initially performed with the millisecond-pulsed and Q-switched ruby lasers and with continuous wave and pulsed argon lasers, the procedure was performed either with no contact lenses or with the plano surface of the Goldmann style contact lens. The Goldmann contact lens has a plano entry surface that is oriented orthogonally to the optical axis of the lens and an exit surface that conforms to the shape of the cornea. When used, the Goldmann contact lens served only to separate the eyelids and to dampen ocular motions. An improvement over the Goldmann lens is the Abraham style iridectomy lens, which converges the laser beam through a 66-diopter button lens placed offcenter on a plano Goldmann carrier lens. The Abraham lens significantly improves the efficacy of laser iridectomy by producing a higher energy density at the iris, while reducing energy density at the cornea and retina. The Abraham iridectomy lens has thus been an important factor in bringing argon laser iridectomy to the status of an accepted standard procedure.
However, even using the Abraham lens, difficulty can occur in perforating very light blue irides, which absorb the laser energy poorly, and thick dark brown irides, which tend to char and shrink. In particular, light blue irides can require high-energy levels that represent a hazard to the macula. The linear incision technique of laser iridotomy and iris sphincterotomy utilize multiple short-duration laser burns to make linear cuts across intrinsic iris tension lines. This method increases the efficiency of iris perforation and produces true iridotomies rather than iridectomies. This method also reduces but does not completely eliminate the difficulties encountered with light blue or thick brown irides.
To avoid the corneal and retinal hazards resulting from high-burn energies, and to further increase the effectiveness of iridotomy and iris sphincterotomy, it would be desirable to selectively increase the energy density at the iris surface above that obtainable with the Abraham iridectomy lens without increasing the actual level of laser energy delivered. Such a selective increase requires additional laser beam convergence to decrease the size of the laser "spot" on the iris. In theory, laser beam convergence is obtainable either by increasing the cone angle of the beam produced by the laser instrument, or by using a strongly converging contact lens. Increasing the cone angle of the laser beam, however, is severely restricted by the constraints of laser design and delivery.
Prior contact lenses with a greater convergence than the Abraham iridectomy lens have, however, met with only limited success. One such lens has its optical center in the center of the carrier ring than offset as in the Abraham iridectomy lens. To bring the optic center over the peripheral iris, either the patient must look down or the lens must be lifted. Downward gaze by a patient is often difficult to maintain under the stimulus of bright laser flashes. On the other hand, lens tilting induces astigmatism and corneal wrinkling. Moreover, the prior lenses are relatively large and markedly reduce the distance between the laser and the lens, thus giving rise to clearance problems between the laser and the lens and between the laser and the nose. It was also thought that increasing the cone angle of a laser beam using a more strongly converging contact lens than the Abraham iridectomy lens would lead to spherical aberrations that would detrimentally affect the desired end result of producing a smaller effective "spot" size at the focal plane of the lens.